The abbreviated term "paper materials", whenever used herein, means all of those materials essentially consisting of cellulose fibers and known, e.g. as waste paper pulp, mechanical pulp, unbleached pulp, bleached pulp, etc. whether or not containing additives and coadjuvants such as binders, fillers, dyes and the like. As is known, paper, paperboard and the like, and relevant applicative products, i.e. products made from paper materials, maintain their combustion once it has started, and because of the lack of self-extinguishing properties their use involves serious risks of fire in many applicative fields. Hence the use of paper materials has been restricted or substantially inhibited in such fields. To obviate the lack of self-extinguishing properties of said materials and products--such as Kraft paper, paper-board, etc.--or at least to reduce the inflammability thereof, various inorganic and/or organic chemical compounds--known as flame retarders--such as, for example: aluminum silicates and phosphates; ammonium sulphates and phosphates along with sodium bicarbonate; ammonium phosphates and polyphosphates, in some cases with melamine; borax-sodium silicate mixtures; salts of phosphorated polyalkyltriazines; amido-polyphosphates; tetrakis-(hydroxymethyl)-phosphonium chloride; hexahydro-triazine phosphonates and derivatives; cellulose ammonium-phosphate with melamine; melamine phosphates; guanyl-urea; copolymers with methyl phosphenyl-isocyanate; diazo-phospholidinones; halogenated polymers; and antimonium aminoalkoxides can be used.
However, these compounds exhibit, depending upon the different utilization modes and media, some drawbacks which do not always render them satisfactory for many applicative fields. For example some of the additives are hygroscopic and easily washable out or swellable by water, so that the physical-mechanical properties of the materials are of low stability in the long run, or because they can evolve, during combustion, very irritant and/or toxic gases, or finally because they are not capable of imparting a sufficient flame retarding effect.
We have developed a flame retarder for other classes of materials substantially different from the paper materials, namely a few types of polymeric material. This retarder is red phosphorus in a form which does not induce in the materials to which it is added, undesirable phenomena of hygroscopicity or instability in the long run any of the mechanical characteristics of practical importance. The red phosphorus powder itself may exhibit drawbacks of hygienic-environmental nature in connection with the fact that red phosphorus, when in contact with the air humidity, generates phosphine (notoriously toxic) during the procedures for incorporating it into the materials to be rendered self-extinguishing, besides during the preceding handlings thereof.